In order to control power output by a power amplifier (PA), most conventional transmitters have a PA control loop, which is a feedback loop that incorporates a detector to measure the power proximate to an antenna of the transmitter. Specifically, most conventional transmitters measure the power levels between the PA and the antenna. The measurement of the output power is used to adjust the gain of the PA so that the PA outputs the desired output power based on the measurement of the output power.
Logarithmic detectors are currently used in the PA control loops of some transmitters. While logarithmic detectors have acceptable dynamic range, they also have undesirable characteristics such as relatively high current drain, large die area, high cost, and low stability at low power levels. In contrast, a linear detector is relatively less sensitive at low power than a logarithmic detector. However, computer simulations of linear detectors incorporated in PA control loops used in conventional transmitters make clear that currently existing linear detectors do not have enough dynamic range to be useful over all desirable output power levels. Thus, there remains a need for a detector circuit having a relatively large dynamic range that is comparable to that of logarithmic detectors, while also having increased sensitivity at low power levels.